How can I find a bug, a roaring sound almost every night. It's in the walls downstairs?

The person moved a few months ago, he said, I'm moving maybe now you can get some sleep when I saw him in the hallway the day he was moving. As he smiled he said, maybe the guy that moves in will be quiet. After telling the Management each time I complained that he wasn't playing anything. He finally admitted it I hear the same roaring sound 4-5 times a week every night. He lived downstairs, he has planted bugs in the walls downstairs apartment the manager looked outside, on the roof. What can I buy to detect where he has planted them because I can't sleep?